HOMEVULNERABILITIESCVE-2026-40561
MEDIUM

CVE-2026-40561

CWE-444Published: May 3, 2026· Updated: May 7, 2026

5.3
CVSS v3.1
EPSS:0.01%probability of exploitation in 30 daysPercentile:1.2th

Official Description

Starlet versions through 0.31 for Perl allows HTTP Request Smuggling via Improper Header Precedence.

Starlet incorrectly prioritizes "Content-Length" over "Transfer-Encoding: chunked" when both headers are present in an HTTP request. Per RFC 7230 3.3.3, Transfer-Encoding must take precedence.

An attacker could exploit this to smuggle malicious HTTP requests via a front-end reverse proxy.

NVD Source

Technical Analysis

CVE-2026-40561 can be exploited remotely over the network without requiring physical or adjacent access, significantly expanding the attack surface for threat actors.

The vulnerability requires no privileges and no user interaction, making it a prime target for automated exploitation campaigns and worm-like propagation.

CVSS v3.1 Vector Breakdown

Exploitability
Attack VectorNetwork
Attack ComplexityLow
Privileges Req.None
User InteractionNone
ScopeUnchanged
Impact
ConfidentialityNone
IntegrityLow
AvailabilityNone
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N

Affected Vendors & Products

kazuho1 product
starlet
Source: NVD CPE · 1 total CPE entries

Exploit & PoC Resources

NO KNOWN EXPLOITNo public exploit confirmed at this time
Exploit-DB
Offensive Security exploit database
GitHub PoC Search
Community PoC repositories
Rapid7 / Metasploit
Metasploit module search
PacketStorm
Security advisories & exploits
NVD Detail
Official NIST entry
MITRE CVE
CVE Program entry
External links open in a new tab. Always verify in a controlled environment before use.

Official Patches & Advisories

PATCHhttps://github.com/kazuho/Starlet/commit/a7d5dfd1862aafa43e5eaca0fdb6acf4cc15b2d0.patch
ADVISORYhttps://datatracker.ietf.org/doc/html/rfc7230#section-3.3.3
ADVISORYhttp://www.openwall.com/lists/oss-security/2026/05/03/1

All References (4)

→
https://datatracker.ietf.org/doc/html/rfc7230#section-3.3.3Third Party Advisory
→
https://github.com/kazuho/Starlet/commit/a7d5dfd1862aafa43e5eaca0fdb6acf4cc15b2d0.patchPatch
→
https://metacpan.org/release/KAZUHO/Starlet-0.32/changes
→
http://www.openwall.com/lists/oss-security/2026/05/03/1Mailing List · Third Party Advisory

Quick Facts

CVE IDCVE-2026-40561
CVSS Score5.3 / 10
SeverityMEDIUM
WeaknessCWE-444
CISA KEVNo
EPSS (30d)0.01%
Affected1 vendor
PublishedMay 3, 2026

Related CVEs (CWE-444)

CVE-2026-41873
9.8
CVE-2026-42581
9.8
CVE-2026-9170
9.8
CVE-2026-13763
9.8
CVE-2026-11541
9.8
CVE-2026-13762
9.8

Recommended Actions

  • →Apply vendor patches immediately
  • →Monitor CVE-2026-40561 in threat intel feeds
  • →Review IDS/IPS signatures for exploitation attempts
Data sourced from NVD (NIST), CISA KEV, and EPSS (FIRST). Analysis generated by CTIWATCH.COM. CVE data is provided under the NVD usage policy.
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